The invention relates to improvements in hydraulic retarders for braking the ends of drive shafts, such as crank shafts or the like, inter alia for vehicles.
In particular, the invention concerns a hydraulic retarder of the kind in which the rotor comprises a rotor shell mounted on a stub which is connected for rotation to the shaft end, the rotor shell being rotatively movable relative to a stator shell forming part of a stator enclosing the rotor, a working liquid being introduced into the rotor shell through the end of the latter from a central intake chamber situated near the axis of the rotor and being discharged therefrom at the larger diameter edge of the shell into a peripheral chamber.
French Pat. No. 2,230,236 discloses such a retarder in which facing zones of the outer surface of the rotor shell and of the inner surface of the stator are shaped to form an annular baffle having a constricted passage, the mean diameter of the constricted passage of the said baffle having a value such that the hydraulic thrusts exerted axially by the working liquid on the two surfaces of the rotor shell are in equilibrium, the contact between the relatively rotating parts of the retarder being limited solely to the sliding contact between a rigid annular bearing surface connected to one of said parts and an annular gasket borne by the other part.
As described in French Pat. No. 2,230,236, the aforementioned construction provides axial balancing which eliminates the need for a thrust bearing for securing the shaft end, thus considerably reducing the overall axial dimensions of the retarder. This advantage is important and often critical.
The proposed construction, however, must be exactly adjusted; this must be done at the factory or in the workshop and non-specialised users must not be allowed to dismantle the retarder themselves.
In the aforementioned construction, since the retarder is mounted at the end of the shaft, the pulley normally provided on the shaft end (e.g. for driving vehicle accessories such as a water pump, a cooling fan, a compressor, a vacuum pump, a dynamo, an alternator or the like) must be mounted between the retarder and the housing from which the shaft-end projects. The retarder stator is then secured to the casing by an apertured structure or cage enclosing part of the pulley.
If the endless belt on the pulley has to be replaced by a new endless belt, inter alia through breakage or excessive elongation, openings must be made in the structure, through which the new belt can be moved from an external position in which it surrounds the structure into an internal position in which it can be mounted without difficulty on the pulley.